A 78-year-old woman was diagnosed with stage III diffuse large B-cell lymphoma, and treated with chemotherapy in 2004. Imaging follow-up was performed by serial 6-month diagnostic PET/CT scans. A PET/CT scan performed in June 2011 showed an unusual hourglass appearance of activity in the pelvis that prompted further investigation. Retrospective review of the prior diagnostic PET/CT scans revealed that the patient had a sliding bladder, located either above or below the pubococcygeal line at different imaging times, but during this scan, the bladder was "caught" moving up to its normal position.